Web tensioning apparatus

ABSTRACT

Apparatus useful in a high speed printing device for automatically tensioning the paper to assure smooth and even movement. Edge perforated paper is employed which is pulled by a tractor drive mechanism from a fan folded supply stack through the automatic tensioning means and past a printing hammer bank. The automatic tensioning means is comprised of a series of elliptical springs mounted on rotatable adjuster rod adjacent one side of the paper and a backup bar having the same surface characteristics as the springs mounted on a resilient pad adjacent the other side of the paper.

I United States Patent H 13,586,149

[72] Inventor Richard H. Miller 1,808,437 6/1931 Roosevelt 197/133 Chatsworth, Calif. 3,176,819 4/1965 Bloom et al... 197/133 [2]] Appl, No. 797,640 3.334,722 8/1967 Bernard 1. 197/133 1 1 Filed d f 12 FORElGN PATENTS 45 Patente une Assign mu Mum Corpomfion 1,022,370 3/1966 Great Britain 197/133 Culver City, Calif. Primary Examiner Ernest T. Wright, Jr.

Att0rneyLindenberg and Freilich [54 WEB TENS'ONING APPARATUS ABSTRACT? Apparatus useful in a high speed printing device W Chin, 4 Drawing Figs. for automatically tenslomng the paper to assure smooth and even movement. Edge perforated paper 15 employed which IS U-S- R pulled a tractor drive mechanism from a fan folded u ply [51] Int. Cl 1. B41 j 15/00 stack through the automatic tensioning means and past a ofsal'ch v i printing hammer bank 'The automatic [ensioning means is comprised of a series of elliptical springs mounted on rotata- [56] Rehrences Cmd ble adjuster rod adjacent one side of the paper and a backup UNITED sTTEs PATENTS bar having the same surface characteristics as the springs 980,273 [I 1911 Ireland 197/133 mounted on a resilient pad adjacent the other side of the Re. 17.747 7/1930 Boyd 197/133 paper.

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WEI! TENSIONING APPARATUS BACKGROUND OF THE INVENTION l. Field of the Invention This invention relates to a web tensioning means particularly useful in a high speed printing device for tensioning paper.

Many high speed printers used in data processing systems employ a hammer bank positioned opposite to a rotating character drum. The hammer bank is comprised of a plurality of individuallyactuatable impact hammers and the character drum has raised characters formed on the peripheral surface thereof. Paper and printing ribbon webs pass between the hammer bank and the drum. In order to print a selected character in a particular position on the paper, the particular hammer disposed adjacent that position is energized when the selected character on the drum moves into alignment therewith. The hammer strikes the paper against the ribbon and drum character to thus print the character on the paper surface adjacent the ribbon. It will be appreciated that in order to achieve high quality printing at high speeds, it is imperative that the paper be moved smoothly and evenly past the hammer bank and then stopped and retained under tension during print operation. Although the difficulties of moving a paper web evenly at high speed are apparent when only a single web is being moved, these difficulties are of course signifi cantly greater when multipart paper is used. Multipart paper consists of several sheets of paper with carbon paper in between and is used, of course, to simultaneously print several copies.

2. Description of the Prior Art High speed printing devices generally employ fan-folded paper having apertures running along both longitudinal edges thereof. The paper is normally driven by upper and lower tractor drive chain pairs. Each drive chain carries a plurality of projections each adapted to engage an edge aperture of the paper. The upper and lower drive chain pairs are respectively disposed above and below the hammer bank. The drive chain pairs are driven in synchronism and thus tend to properly tension and evenly move the paper. In order for this type of paper drive system to operate satisfactorily at very high speed with multipart paper, it is imperative that it be exceedingly accurate and that the paper be located accurately relative to the tractors by the operator. 1f the system is not sufficiently accurate, the chain projections may become disengaged from the paper apertures, thus permitting the paper to become skewed relatively tothe aligned hammer tips thereby, of course, adversely affecting print quality and ultimately causing a paper jam. With multipart paper, the differences between the drag forces normally seen by the first and last layers of paper sometimes causes slipping of the layers relative to one another thereby also adversely affecting print quality. In order to avoid these problems, it is essential that the paper drive system be very accurate and this in turn causes the conventional paper drive system to be very costly and burdensome to the operator.

SUMMARY OF THE INVENTION The present invention is primarily directed to an automatic web tensioning apparatus which is particularly useful in a high speed printing device. Use of a tensioning apparatus in accordance with the invention, in a high speed printer, enables satisfactory performance to be achieved using a less costly paper drive system requiring fewer operator adjustments.

Briefly, in accordance with the present invention, a web tensioning apparatus is provided which includes one or more deformable springs mounted on a rotatable adjuster rod adjacent one face of the web and a backup bar mounted on a resilient pad adjacent the other face of the web. The web is adapted to pass between and be engaged by the springs and backup bar.

In accordance with a significant feature of the invention, the same surface characteristics (coefficient of friction) are selected for both the spring and backup bar to thus produce the same drag forces on the front and back layers of the multipart paper, to thereby minimize the force gradient through the paper layers.

In a preferred embodiment of the invention, a plurality of elliptical leaf springs are mounted on a rotatable adjuster rod which is supported opposite to a backup bar mounted on a resilient pad. The springs and backup bar are formed of the same material, e.g. copper, and thus exhibit the same coefficient of friction. The elliptical springs are mounted so that translational movement in a direction extending across the paper web and perpendicular to the direction of movement thereof is restrained. The springs however are able to exhibit resilient deflection in a direction parallel to the web movement and in a direction toward and away from the plane of the web. The backup bar is mounted so that translation thereof in a direction parallel to the plane of the web is prevented. However, resilient deflection toward and away from the web is permitted.

In use, the elliptical springs cause a dynamic downward force on the paper due to elastic deformation imposed upon the springs when the paper travels upward therepast. This downward force tensions all sheets of paper as well as compensates for any oscillatory overtravel imposed by the main paper drive system. Use of a tensioning apparatus in accordance with the invention reduces the accuracy requirements of the paper drive system and thus enables a less costly drive system to be used. The alignment of the paper supply stack to the paper drive system becomes far less critical due to the ironing action of the tensioning apparatus of the paper.

The novel features of the invention are set forth with particularity in the appended claims. The invention will best be understood from the following description when read in conjunction with the accompanying drawing.

' BRIEF DESCRIPTION OF THE DRAWING FIG. I is a perspective view of a high speed printer incorporating a web tensioning apparatus in accordance with the invention shown in open position;

FIG. 2 is a sectional view of the high speed printer of FIG. I shown in closed position and taken substantially along the plane 2-2;

FIG. 3 is an enlarged sectional view taken along the plane 3-3 of FIG. 2 illustrating the action of the web tensioning apparatus in accordance with the present invention; and

FIG. 4 is a sectional view of the printer in closed position illustrating the web paths.

DESCRIPTION OF THE PREFERRED EMBODIMENT Attention is now called to FIG. 1 of the drawings which illustrates a high speed printing apparatus incorporated a web tensioning assembly in accordance with the present invention. The printing apparatus of FIG. 1 is basically comprised of a first frame 10 supporting a bank of individually actuatable impact hammers 12. The hammer tips 14 are disposed in horizontal alignment. The number of hammers I2 normally provided is equal to the maximum number of characters it is desired to print in a single line. Thus, if it is desired to print lines having up to character positions, then it is normally necessary to provide 120 hammers 12.

The frame 10 also supports a paper drive tractor mechanism including first and second endless drive chains 16 and 18. Each of the drive chains 16 and 18 carries a plurality of projections 20, each adapted to engage an edge aperture 21 formed in fan-folded edge perforated paper. A paper supply stack 22 is normally stored on the base 24 of the frame 10. The projections 20 carried by the chains 16 and 18 engage the edge apertures 21 of the fan-folded paper to thus pull the paper from the supply stack 22 past the hammer bank 12. In use, the endless drive chains 16 and 18 are continuallydriven by a drive train including a motor 26 driving a belt 28 which in turn rotates a shaft 30 to move the drive chains 16 and 18 in synchronism.

The printer apparatus of FIG. I also includes a hinged frame or gate 32 which is hinged relative to the first frame for movement about a substantially vertical axis. The frame 32 supports a character drum 34 (FIG. 4) for rotation about its own axis. The drum 34 is driven by motor 36 and is supported behind a printing ribbon web 38. The circumferential surface of the drum 34 is provided with a plurality (e.g. 120 of tracks 37, each track including a set of raised printing characters 39. Each track corresponds to a different character position in a line of print and the number of different characters 39 in each track 37 of course determines the number of different characters which can be printed in the corresponding character position.

In the use of the apparatus of FIG. I, the gate 32 is moved from the open position shown to a closed position in which the printing ribbon web 38 is immediately opposed to the hammer bank 12. The paper is drawn by the drive chains l6 and 18 from the supply stack 22 through the passageway between the hammer bank 12 and printing ribbon 38. Printing is accomplished by incrementally moving the paper web, line by line, and by actuating each hammer 12 when the appropriate character 39 on the drum 34 moves into alignment therewith to thus propel the hammer 12 against the paper to urge the paper against the ribbon 38 and drum 34.

From the foregoing brief description of the operation of the apparatus of FIG. 1, it will be readily recognized that in order to achieve high quality printing, it is essential that the character drum 34 be precisely positioned with respect to the hammer bank 12. On the assumption that the individual hammers I2 can all be precisely positioned with respect to the frame 10 and that the axis of the character drum 34 can be precisely located with respect to the gate 32, it is then merely necessary to precisely position the gate 32 with respect to the frame 10 when they are in closed operative relationship. In order to assure this, the printing apparatus of FIG. 1 includes a latch assembly comprised of a precisely mounted rotatable latch shaft 40 carried by gate 32 and a precisely mounted bracket member 42 having a receptacle 43 for receiving the shaft 40, mounted on the frame I0.

In order to assure high quality printing, it is essential that the paper be moved smoothly and evenly from the supply stack 22 past the hammer bank 12. That is, if the movement of the paper is somewhat skewed, then the resulting print will also be somewhat skewed. Accordingly, it is essential that the movement of the paper 22 be precisely perpendicular with respect to the row of aligned hammer impact tips 14. In order to assure that successively printed lines are evenly spaced, and that each copy simultaneously printed by utilizing multipart paper is identical, it is important that all the layers of the multipart paper he moved in unison. In other words, it is essential that the layers of the multipart paper do not slip relative to one another. Another important criteria for high quality printing is the stopping and tensioning of the paper web. The drum 34, while rotating, will pull the paper out of alignment 34, while rotating, will pull the paper out of alignment if it is not secured and tensioned.

The present invention is primarily directed to a web tensioning apparatus comprised of a spring assembly 50 mounted on the frame 10 below the hammer bank 12, or remote from the drive chains 16 and 18, and a backup portion 52 mounted on the gate 32 opposite to the spring portion 50.

The spring portion 50 includes an adjuster rod 54 joumaled for rotation in mounting blocks 56 and 58 fixedly mounted on the frame 10. The collar 60 of a flag member 62 is secured to one end of the rod 54. The flag member 62 includes a flag portion 64 adapted to be abutted by the free end of an adjusting screw 66 having a knurled knob 68. The shank of the adjusting screw 66 is threaded through an opening 70 formed in a depending leg 72 of the mounting block 56. A spring 74 connects the flag 64 to the depending leg 72. It will be appreciated that by turning the knurled knob 68 of the adjusting screw 66, the rotational orientation of the rod 54 can be selectively established.

In accordance with the preferred embodiment of the invention, three elliptical leaf springs 75 are mounted on the rod 54 equally spaced from one another The elliptical spring 75 are preferably formed from beryllium copper annealed stock (e.g., 0.007 inch thick and one-halfinch wide). A length of the annealed stock is formed into an ellipse and then heat treated to fix its spring characteristics. The perimeter of the elliptical springs 75' is, of course, comprised of first and second long portions and 82 of relatively large radius of curvature and third and fourth shorter portions 84 and 86 of relatively small radius of curvature. The portions 82 of each spring 75 are bolted to the adjuster rod 54 by bolts 88 and nuts 90, within slots 92 formed in the adjuster rod 54. The portions 80 of the springs 75 are thus free and project toward the frame 32.

As previously pointed out, the frame 32 carries a backup portion 52 of the web tensioning apparatus. The backup portion 52 is comprised of a backup strip 94, preferably formed of beryllium copper, adhered to a resilient pad 96, for example, formed of polyethylene foam. The pad 96 is secured to a mounting bar 98 fastened to the gate 32.

As shown in FIG. 2, in operative relationship the portion 80 of each spring 75 provides a first paper engaging surface disposed opposite to a second paper engaging surface defined by backup strip 94. In accordance with a feature of the invention, the springs 75 and backup strip 94 are formed of the same material e.g. copper, so as to define the same surface coefficient of friction. By selecting the strip 94 and spring 75 to have the same coefficient of friction, they will produce the same drag force on the first and last layers of multipart paper as the paper is pulled through the passageway defined therebetween by the drive chains 16 and 18. Accordingly, the force gradient through the several layers of the multipart paper will be reduced thereby considerably reducing the likelihood of slippage relative to one another.

When the web tensioning apparatus is in operative position as shown in FIG. 2, but without paper passing therethrough, the first paper engaging surfaces 80 provided by springs 75 will lie in a plane defining a first axis extending parallel to the movement of the paper and a second axis extending perpendicular to the movement of the paper. The construction and mounting of the springs 75 enables the first paper engaging surfaces 80 to deflect in a direction substantially parallel to the first axis, or in other words, parallel to the direction of paper movement. Additionally, the spring construction enables deflection of the first paper engaging surface 30 along a third axis perpendicular to the plane defined by the first and second axes. The mounting of the springs 75, however, restrains translation of the first paper engaging surfaces 80 in a direction parallel to the second axis or in other words across the paper. As a consequence, the springs 75 tend to iron out the paper and prevent skewed movement thereof. It will be appreciated that the backup strip 94 is able to deflect only in a direction parallel to the third axis, or in other words, perpendicular to the surface defined thereby.

In use, the elliptical springs 75 produce a dynamic downward force on the paper as the paper is drawn upwardly through the passageway defined between the backup strip 94 and the spring portions 80. More particularly, the upward movement of the paper elastically deforms the spring 75 from the solid line position shown in FIG. 3 to the dotted line position represented therein. This dynamic downward force tensions all the layers of multipart paper as well as compensates for any oscillatory overtravel imposed by the main paper drive system.

From the foregoing, is should be appreciated that a web tensioning apparatus has been disclosed herein for applying suitable tension to a moving web in order to cause it to move smoothly and evenly past an operational station such as is defined by the row of aligned hammer tips and to stop and retain it under tension in a repeatable manner. Although the particular embodiment of the invention disclosed herein constitutes a high speed printer employing edge perforated paper, the utility of the invention in other environments and with other types of webs should be readily recognized.

What I claim is:

1. Web tensioning apparatus useful in combination with a drive system for pulling a web, said tensioning apparatus comprising:

an elliptical leaf spring providing a first web engaging surface lying substantially in a plane defined by first and second orthogonal axes;

means mounting said spring for restraining translation of said first web engaging surface only in a direction parallel to said first axis to thus permit resilient deflection of said first web engaging surface in a direction parallel to said second axis and parallel to a third axis orthogonal to said first and second axes;

backup means providing a second web engaging surface extending substantially parallel to said first web engaging surface;

means mounting said backup means for restraining translation of said second web engaging surface only in a direction parallel to said first and second axes to thus permit resilient deflection of said second web engaging surface in a direction parallel to said third axis; and

means supporting said spring and backup means with said first and second web engaging surface opposed to one another.

2. The web tensioning apparatus of claim 1 wherein said first and second web engaging surfaces exhibit substantially the same coefficient of friction.

3. The web tensioning apparatus of claim 1 wherein said elliptical leaf spring has first and second perimeter portions of lesser radius of curvature and third and fourth perimeter portions of greater radius of curvature.

4. The web tensioning apparatus of claim 3 wherein said means mounting said spring includes a rotatable adjuster rod; and

means securing said spring third perimeter portion to said adjuster rod. g

5. The web tensioning apparatus of claim 4 including means for adjusting and maintaining the rotational orientation of said adjuster rod.

6. The web tensioning apparatus of claim 1 wherein said backup means includes a fiat strip adhered to a resilient pad.

7. A high speed printing device comprising:

a movable character surface;

a plurality of hammers supported opposite to said character surface and spaced therefrom to define a paper passageway therebetween;

a paper drive means disposed proximate to the exit of said passageway for pulling paper therethrough; and

a paper tensioning means disposed proximate to the entrance of said passageway for tensioning said paper, said tensioning means including:

I. an elliptical leaf spring including a first paper engaging surface lying substantially in a plane defined by first and second orthogonal axes;

2. means mounting said spring for restraining translation of said first paper engaging surface only in a direction parallel to said first axis to thus permit resilient deflection of said first paper engaging surface in a direction parallel to said second axis and parallel to a third axis orthogonal to said first and second axes;

3. backup means providing a second paper engaging surface extending substantially parallel to said first paper engaging surface;

4. means mounting said backup means for restraining translation of said second paper engaging surface only in a direction parallel to said first and second axes to thus permit resilient deflection of said second paper engaging surface in a direction parallel to said third axis;

and 5. means supporting said spring and backup means with said first and second paper engaging surfaces opposed to one another.

8. The printing device of claim 7 wherein said passageway defined between said hammers and said character surface extends in a plane substantially parallel to said first and second paper engaging surfaces.

9. The printing device of claim 7 wherein said first and second paper engaging surfaces exhibit substantially the same coefficient of friction.

10. The printing device of claim 7 wherein said elliptical leaf spring has first and second perimeter portions of lesser radius of curvature and third and fourth perimeter portions of greater radius of curvature. 

1. Web tensioning apparatus useful in combination with a drive system for pulling a web, said tensioning apparatus comprising: an elliptical leaf spring providing a first web engaging surface lying substantially in a plane defined by first and second orthogonal axes; means mounting said spring for restraining translation of said first web engaging surface only in a direction parallel to said first axis to thus permit resilient deflection of said first web engaging surface in a direction parallel to said second axis and parallel to a third axis orthogonal to said first and second axes; backup means providing a second web engaging surface extending substantially parallel to said first web engaging surface; means mounting said backup means for restraining translation of said second web engaging surface only in a direction parallel to said first and second axes to thus permit resilient deflection of said second web engaging surface in a direction parallel to said third axis; and means supporting said spring and backup means with said first and second web engaging surface opposed to one another.
 2. The web tensioning apparatus of claim 1 wherein said first and second web engaging surfaces exhibit substantially the same coefficient of friction.
 2. means mounting said spring for restraining translation of said first paper engaging surface only in a direction parallel to said first axis to thus permit resilient deflection of said first paper engaging surface in a direction parallel to said second axis and parallel to a third axis orthogonal to said first and second axes;
 3. backup means providing a second paper engaging surface extending substantially parallel to said first paper engaging surface;
 3. The web tensioning apparatus of claim 1 wherein said elliptical leaf spring has first and second perimeter portions of lesser radius of curvature and third and fourth perimeter portions of greater radius of curvature.
 4. The web tensioning apparatus of claim 3 wherein said means mounting said spring includes a rotatable adjuster rod; and means securing said spring third perimeter portion to said adjuster rod.
 4. means mounting said backup means for restraining translation of said second paper engaging surface only in a direction parallel to said first and second axes to thus permit resilient deflection of said second paper engaging surface in a direction parallel to said third axis; and
 5. means supporting said spring and backup means with said first and second paper engaging surfaces opposed to one another.
 5. The web tensioning apparatus of claim 4 including means for adjusting and maintaining the rotational orientation of said adjuster rod.
 6. The web tensioning apparatus of claim 1 wherein said backup means includes a flat strip adhered to a resilient pad.
 7. A high speed printing device comprising: a movable character surface; a plurality of hammers supported opposite to said character surface and spaced therefrom to define a paper passageway therebetween; a paper drive means disposed proximate to the exit of said passageway for pulling paper therethrough; and a paper tensioning means disposed proximate to the entrance of said passageway for tensioning said paper, said tensioning means including:
 8. The printing device of claim 7 wherein said passageway defined between said hammers and said character surface extends in a plane substantially parallel to said first and second paper engaging surfaces.
 9. The printing device of claim 7 wherein said first and second paper engaging surfaces exhibit substantially the same coefficient of friction.
 10. The printing device of claim 7 wherein said elliptical leaf spring has first and second perimeter portions of lesser radius of curvature and third and fourth perimeter portions of greater radius of curvature. 